Honey bees use floral odors to help find and identify the flowers from which they forage, but the fumes from diesel exhaust can change the way flowers smell.

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For a study published in Scientific Reports, researchers mixed eight chemicals found in the odor of oil rapeseed flowers with clean air and with air containing diesel exhaust.

Six of the eight chemicals reduced (in volume) when mixed with the diesel exhaust air and two of them disappeared completely within a minute, meaning the profile of the chemical mix had completely changed. The odor that was mixed with the clean air was unaffected.

Furthermore, when the researchers used the same process with NOx gases (nitric oxide and nitrogen dioxide), which is found in diesel exhaust, they saw the same outcome, suggesting that NOx was a key facilitator in how and why the odor’s profile was altered. The changed chemical mix was then shown to honey bees, which could not recognize it.

Exceptional learners

“Honey bees have a sensitive sense of smell and an exceptional ability to learn and memorize new odors. NOx gases represent some of the most reactive gases produced from diesel combustion and other fossil fuels, but the emissions limits for nitrogen dioxide are regularly exceeded, especially in urban areas,” says Tracey Newman, a neuroscientist at the University of Southampton.

“Our results suggest that that diesel exhaust pollution alters the components of a synthetic floral odor blend, which affects the honey bee’s recognition of the odor. This could have serious detrimental effects on the number of honey bee colonies and pollination activity.”

“Honey bee pollination can significantly increase the yield of crops and they are vital to the world’s economy—£430 million a year to the UK alone. However to forage effectively they need to be able to learn and recognize the plants,” says Guy Poppy, professor of ecology.

“The results indicate that NOx gases—particularly nitrogen dioxide—may be capable of disrupting the odor recognition process that honey bees rely on for locating floral food resources. Honeybees use the whole range of chemicals found in a floral blend to discriminate between different blends, and the results suggest that some chemicals in a blend may be more important than others.”